I'm not so sure that Warner would actually care very much for the secret wishes of some fans. For them it would not matter what some "fans" want unless they risk a major PR disaster!

Compared to the vast crowd of paying customers, a few fans, especially as long as they stay silent and passive, will not matter for their business decisions!

But back to your main question:

I highly doubt that PJ or the technical stuff can do anything significant to influence the decision making at this point!

The government could cough up a couple of millions to "ease" some decision - but they can't really change anything and even offering to change laws cannot actually be considered in the decisions by 'Warner that have to be made right now, since it would take time (years?) of parliamentary process, have an unsure result (will it actually pass?), and simply won't be in time to be of any significance right NOW when now is the time these decisions have to be made.

The only ones, I think, who could actually do something (except for the fans to threaten to cause an uprising and a PR and box office disaster!) would be the actors. The actors in NZ and worldwide (since the blacklisting was an internationally organized union boycott call!) to state in a convincing manner that they, the actors, would never follow any boycott call concerning The Hobbit, would undermine and thwart any further attempt to do so and would even risk internal repression from unions in order to safeguard the making of The Hobbit in NZ, if any "union" ever would dare to threaten the production of The Hobbit again.

But how likely is that?

And that the Whipping Guy has left the country only tells me that he: a) has done the damage he could b) is not really interested in cleaning up or even only calming down the mess he has caused.

(He might not have achieved his goals but he sure as hell gives a s#*t about the consequences of his campaign!)

What anybody can do?

I think it's definitely down to the good will of Warner and whether they will predominantly listen to their accounting numbers or the spirit of a movie. (And guess how bleak that perspective looks!)

The only ones (apart from "all" the individual actors worldwide) who have not already thrown everything in they have, are the fans worldwide.

The prospect audience of The Hobbit is the only group that (publicly) remained silent until now and it's the only group that could actually significantly still matter now to influence Warners decisions! .